How to compare transfer speeds on Windows and macOS

A USB drive or SD card can seem faster on one computer than another. The difference might come from the drive, the USB port, an adapter, or the way each computer handles the test.

Use the same device and a consistent setup on both computers. TooLab's USB & SD Speed Test measures read and write speed, so you can compare each result instead of relying on how long a file copy seems to take.

Compare the speeds on both computers

1. Open the USB & SD Speed Test on the first computer. Connect the USB drive or card reader, and follow the prompts to select the removable drive and allow access if asked.
2. Keep the drive, cable, card reader, and adapter the same. Use a comparable USB port on each computer, and make sure the drive is not full or busy with another transfer.
3. Run the test and note the read speed and write speed separately. Read speed is how quickly the computer can get data from the drive. Write speed is how quickly it can put data onto the drive.
4. Eject the drive safely, connect it to the second computer, and repeat the test with the same browser if possible. Keep other conditions as similar as you can.
5. Run each test a second time after the first run has finished. Compare the repeated results, not just one number, since background activity can change a measurement.

Do not unplug the drive while a test is running. If the browser cannot access it, check for a permission prompt or a message explaining what access is needed.

What the results mean

Both computers show similar read and write speeds

The drive and connection may be setting the limit, rather than either operating system. A basic flash drive can be much slower than a fast USB port, so a faster port will not necessarily improve its measured speed.

One computer is slower in both directions

That points to a difference in the connection or computer, but it does not prove the computer is faulty. Check whether you used a hub, adapter, or slower port on that computer. A different USB port can have a large effect.

Read speeds are close, but write speeds differ

The drive may handle reads consistently but write at different rates depending on the computer, file system, or available space. Flash drives can also slow during longer writes as their fast temporary cache fills.

The results vary a lot between repeat runs

Something may be using the drive or computer in the background, or the drive may be getting warm. Close file transfers and backup jobs, wait a few minutes, then repeat the test. A large difference between runs is a reason to retest before drawing a conclusion.

The test cannot access the drive or write to it

Check that the drive is mounted, that the browser has permission, and that the drive is writable. macOS can usually read NTFS drives but does not normally write to them without extra software. That can prevent a write test even when the drive itself is working.

How to make the comparison fair

1. Close other transfers. Pause file copies, backups, sync jobs, and downloads using the drive. On both computers, let the test run without other heavy disk activity.
2. Use the same connection path. Plug the drive directly into each computer when possible. If you need an adapter or hub, use the same one on both. Try another port if one computer is unexpectedly slow.
3. Keep the browser consistent. Use the same browser on both computers if available, and close unnecessary tabs. Browser and computer activity can affect a browser-based measurement.
4. Check the drive's format and free space. Windows 11 includes Disk Management, which you can open by right-clicking Start and choosing Disk Management. On macOS, open Applications › Utilities › Disk Utility and select the external drive to see its format and capacity. Do not erase or reformat a drive just to run a comparison. Formatting can delete its contents.
5. Compare the same units. Check that both results use the same unit, such as MB/s. MB/s means megabytes per second. Mb/s means megabits per second, and one megabyte is eight megabits.
6. Test another drive or port. If one computer remains slower, try a second drive on both systems. If only one drive is slow on one port, the drive or port is a stronger suspect than the operating system.

When the drive or port may be faulty

If a drive gives inconsistent results, disconnects, or produces errors on both computers, copy off any important files before doing more tests. Check it in another port and, if possible, with another computer. A drive that repeatedly fails or disconnects across different systems may be damaged and should not be trusted with the only copy of important data.

If the same drive is consistently slow only through one port or adapter, test a different port or adapter before replacing the drive. If the problem follows a particular USB port with multiple devices, the port or computer may need service.

Why a speed test differs from copying a folder

A speed test gives you a controlled read and write measurement. Copying a folder with thousands of small files can be slower because the computer has to handle each file and its details, not just move a continuous stream of data. Copying one large video file is a closer comparison to a sequential speed measurement, but it can still vary with caching, file format, and background tasks.

Use the test to compare the same drive under similar conditions. Treat small differences as normal variation, and investigate large, repeatable gaps by changing one part of the setup at a time.